98 Oliver . — On the Obliteration of 
thick walls, the width of the zone depending on the age of 
the part. These tubes are true sieve-tubes , and resemble to 
an extraordinary degree those of Cucurbita . Will 1 , in an 
admirable paper on the anatomy of Macrocystis luxurians , 
describes these sieve-tubes carefully 2 . He did not, however, 
find any bodies of the nature of callus-plates, which we shall 
show are always developed. Nor does he, oddly enough, 
make any mention of the trumpet-hyphae in the central 
medulla. These he seems quite to have overlooked. 
Nereocystis has not, so far as I am aware, been carefully 
investigated before, though Postels and Ruprecht 3 , in their 
account of the sea-weeds obtained in the Liitke expedition of 
r 826-9, give one or two rough figures of its anatomy, showing 
trumpet-hyphae. In it I find the tissues to be arranged very 
much as in Macrocystis , a central medulla with trumpet- 
hyphae, and this surrounded by a zone of true sieve-tubes. 
In Nereocystis as in Macrocystis callus is formed in the true 
sieve-tubes as well as in the trumpet-hyphae. In the trumpet- 
hyphae of other Laminarieae I have so far (with one excep- 
tion) been unable to discover any callus. I will now proceed 
to describe the sieve-tubes and trumpet-hyphae of these two 
genera. 
Nereocystis Liitke ana, Post, et Rupr. 4 , is found along the 
North-west coast of North America, at Norfolk Sound 
and elsewhere. The only good general account is that 
by Mertens 5 , who was its first scientific discoverer and named 
it provisionally Fucus Liitke anus. When young the plant 
consists of a dichotomously branched c root 5 with stem some 
1 H. Will, Zur Anatomie von Macrocystis luxurians, in Bot. Ztg. 1884, p. 
801. 
2 I am informed by my friend Dr. D. H. Scott, that in reality Will is not to 
be regarded as the discoverer of these sieve-tubes. They were previously found 
by Professor T. J. Parker of Otago, New Zealand, but I have been unable to 
confirm the reference from the inaccessibility of the Journal in which they 
are described. 
3 Postels et Ruprechts, Illusfcrationes Algarum, t. 39. 
i Postels et Ruprechts, Op. cit., p. 9. tt. 8-9. 
5 H. Mertens in Linnaea, 1829, p. 48. Translated in Hook. Bot. Misc. iii. 
(1833), p. 3. Cf. also Harvey, Nereis Boreali- Americana, p. 85. 
